Arrests by the embattled Street Crime Unit were down last week, the first week the officers patrolled in uniform, figures obtained by The Post show.

But Mayor Giuliani insisted that arrests by the unit had begun to rebound in the last few days.

Sources told The Post the number of arrests last week was 11, compared to 18 the previous week.

At its height, the 380-member SCU has made as many as 70 arrests in a week.

Giuliani, noting the number of arrests by the unit fell 70 percent since four of its members killed unarmed immigrant Amadou Diallo, said yesterday, ”The Street Crime Unit is back again being somewhat more engaged than they were before.

”It’s changed a little in the last week … they [arrests] have [gone up] the last four or five days,” he said.

A breakdown could not be obtained to determine the number of arrests in the last several days.

The mayor added, ”I understand that if the police do not feel that they are appropriately supported – and I emphasize appropriately supported – then there is going to be almost inevitably a sense of backing off a little bit to protect yourself.

”[Police Commissioner Howard Safir] said he was concerned about the drop off of arrests [and] that was one of the reasons he put them back in uniform, so they would feel more confidence in undertaking police activity.”

Giuliani said a recent increase in murders occurred ”disproportionately in those areas where the Street Crimes Unit stopped making arrests.”

”Their arrests are down almost 70 [percent], their searches and stop activities are down probably more than that and the places where there seems to be a withdrawal of activity there’s an increase in murder,” the mayor said.

In other developments:

* City officials today will announce new training for cops on stop-and-frisk operations. The cops will be taught to do a better job explaining to people why they were stopped and searched.

* Giuliani, who has balked at any meeting with the Rev. Al Sharpton, yesterday had a City Hall sit-down with a group of black leaders – including Sharpton’s 1997 mayoral campaign manager.

Jacques DeGraf, a minister and manager of Sharpton’s Democratic primary run, was among five members of the organization One Hundred Black Men who spent an hour with Giuliani.

”We had a fairly candid exchange,” said DeGraf, a vice-president of the group. ”It never came up, but I’d be surprised if he didn’t know that I worked with Rev. Sharpton.”

DeGraf said the mayor listened ”attentively” as they called for stepped up recruiting of minorities for the NYPD and as they described the increasing level of tension between cops and their communities.